In natural breathing, the diaphragm contracts and flattens, and external intercostal muscles contract to lift the ribcage up and outward. These two processes expand the volume of the thoracic cavity, thereby inducing a decrease in intrathoracic pressure (i.e., induces negative pressure within the cavity). As a result, air flows from the atmosphere into the lungs due to the induced negative pressure within the cavity. This phenomenon is called Negative Pressure Ventilation (NPV).
When the brain is unable to transmit electrical signals, such as in the case of traumatic injuries, normal breathing stops and artificial forms of ventilation are used to resuscitate patients. The current standard for assisted ventilation during resuscitation is a form of Positive Pressure Ventilation (PPV) whereby air is pushed into the lungs through mouth-to-mouth breathing or through an endotracheal tube. Such devices include for example, a bag valve mask (typical part of a crash or ambulance kit) and mechanical ventilators whereby compressed oxygen/air is delivered pneumatically through nasal intubation or tracheotomy (e.g., see FIG. 1). In the mouth-to-mouth breathing technique an impedance threshold valve (ITV) may be used, which prevents air from entering the lungs during the decompression phase of CPR.
As PPV increases the pressure in the patient's airways, the resultant increased intra-thoracic pressure has been shown to have many detrimental hemodynamic effects such as decreased venous return and decreased cardiac output. It also has been found that PPV also can result in increased intra-luminal central venous pressure and increased intracranial pressure. The increased intracranial pressure ultimately leads to decreased cerebral perfusion pressure and decreased blood flow to the brain.
Ample clinical studies suggest that it is the hours immediately following trauma, in particular, where use of PPV has the strongest likelihood of brain damage. For example, in the United States alone, 1.5 million Americans suffer from traumatic brain injuries every year. Among these patients, increased intracranial pressure in the hours immediately following trauma accounts for 50% of deaths.
In U.S. Pat. No. 2,532,788, there are found methods and devices for stimulating a physiological functions of an individual, more specifically, for inducing of respiration. As indicated therein, prior techniques for inducing respiration included using the PPV technique or by enclosing the entire body or chest with the exception of the head and neck within an enclosure (i.e., iron-lung) and cyclically pressurizing the enclosure (resulting chest movement simulates natural breathing).
The methodology described in this patent includes placing a probe within the body so it is in physical contact with the sheath of the phrenic nerve. In this way, electrical potential applied to the probe, in the form of pulses, stimulates the phrenic nerve causing movement of the diaphragm as would occur in natural breathing. In another technique, a pair of electrodes are located on the neck so that one electrode is applied to the skin overlying the course of the phrenic nerve so that the electrical potential is applied to the nerve trunk through the skin. The second electrode is placed on the back of the neck, so that the resultant path of the current includes a portion of the phrenic nerve or one of its anatomical roots.
An anatomical view of the neck highlighting the location of one of the phrenic nerves in the neck is shown in FIG. 2. The phrenic nerve is made up mostly of motor nerve fibers for producing contractions of the diaphragm. It also provided sensory innervation for many components of the mediastinum and pleura, as well as the upper abdomen, especially the liver and the gall bladder.
As is known to those skilled in the art, phrenic nerve pacing (PNP) or diaphragm pacing (earlier referred to as electrophrenic respiration) was developed, in which electrical pulses are rhythmically applied to the diaphragm thereby causing respiration for patients that otherwise would be dependent upon a mechanical ventilator. In this technique, surgery is performed so as to place an electrode around and in physical contact with the phrenic nerve either in the neck (cervically) or in the chest (thoracically). The electrode is connected to a RF receiver implanted under the skin and an external transmitter sends RF signals to the receiver. Such devices generally fall under the category of a Class III medical device such as a pacemaker.
It thus would be desirable to provide a portable device/apparatus for stimulating one or both of the phrenic nerves so that a trauma patient can breathe by natural contraction of the diaphragm, avoiding traditional positive pressure ventilation that result in negative hemodynamic effects. Also featured are methods for localizing the phrenic nerve and inducing negative pressure respiration in such a trauma patient. It would be particularly desirable to provide such a device and method that would be minimally invasive particularly in comparison to prior art devices. Such devices/apparatuses preferably would be deployable in field emergency settings and work well with existing EMT protocols and equipment.